Herbicidal 4-((benzimidazol-1-yl)phenoxy)alkanoic acids, esters and salts

ABSTRACT

Certain 4-((benzimidazol-1-yl)phenoxy)alkanoic acids, esters and salts, useful as herbicides.

DESCRIPTION OF THE INVENTION

It has been found that certain 4-(benzimidazol-1-yl)phenoxy)alkanoicacids, esters and salts adversely affect the growth of plants to whichthey are applied, and thus are of interest for controlling the growth ofunwanted plants. These compounds are described by the formula: ##STR1##wherein n is 1 and X is trifluoromethyl, R is hydrogen, methyl or ethyl;R¹ is methyl, ethyl or methoxymethyl; m is 0, 1 or 2; and R² ishydrogen, alkyl of from one to four carbon atoms, and when R² ishydrogen, the alkali metal and ammonium (N(R³)₃) salts, wherein each R³is hydrogen or alkyl of from one to six carbon atoms.

Highest phytotoxicity appears to reside in the subclass of the classdefined in Formula I wherein the trifluoromethyl moiety is bonded to thering at the 5-position, R and R¹ each represents methyl, m is 0, and R²represents hydrogen, methyl or ethyl, so that this subclass forms apreferred aspect of the invention.

The compounds of Formula I are prepared by treating an ester of theformula ##STR2## with a trialkyl ester of an orthoalkane acid, such astriethyl orthoformate (R=H), orthoacetate (R=methyl) and orthopropionate(R=ethyl). The treatment is conviently effected by heating the ester ofFormula II with an excess of the orthoalkane ester, the latter beingused as solvent as well as reactant. Conduct of the treatment inparticular instances is described in the Examples, hereinafter.

Compounds of Formula II are prepared by reduction of the correspondingnitrophenyl compounds of the formula: ##STR3## The reduction isconveniently effected by treatment of a solution of the nitro compoundin an inert solvent such as tetrahydrofuran with hydrogen under pressurein the presence of a catalyst, such as charcoal impregnated with 10%w ofpalladium, using a suitable apparatus, such as a Parr shaker. Use ofthis method, too, in particular instances is described in the Examples.

The nitro compounds of Formula III, as a general class, and methods forpreparing them, are described in U.S. Pat. No. 4,259,105. As describedin the patent, two general methods can be used to prepare compounds ofFormula III.

(1) Treatment of a phenol ##STR4## with a haloalkanoic acid or ester##STR5## and

(2) Treatment of a halide ##STR6## with an amine ##STR7##

Techniques by which the reaction of the two materials can be conductedare described in the patent and are illustrated in particular instancesin the Examples hereinafter.

Typical precursors to the phenols, halides and amines, and theirpreparation, are described in the patent and their preparation inparticular instances is described in the Examples hereinafter.

Generally, the phenols (Formula IV) are prepared by effecting reactionbetween a halide ##STR8## and p-aminophenol ##STR9##

The amine precursors (Formula VII) are prepared by effecting reactionbetween 4-nitrophenol and an alkyl ester of a haloalkanoic acid (FormulaV), in a solvent and in the presence of an alkaline condensing agent,such as potassium carbonate, and then catalytically reducing them withhydrogen to form the corresponding amine.

Preparation of the precursor wherein R¹ =methoxymethyl is described inExample 10, hereinafter.

In the case where m=2, an alternate method of preparing the precursor(Formula II) is illustrated in Example 12, hereinafter: the alkenoicacid counterpart is first prepared and catalytically hydrogenated toboth saturate the olefinic double bond and reduce the nitro moiety tothe amino moiety.

Conversion of an acid (R² =H) to an ester (R² =alkyl) and vice versa iseffected by conventional methods, illustrated in the Examples,hereinafter.

The salts of the subclass of the compounds of Formula I wherein R² ishydrogen are prepared by conventional methods.

Synthesis and isolation of individual compounds of Formula I inparticular instances are described in the following examples. In eachcase, the identity of the product, and of any intermediate in volved,was confirmed by appropriate chemical and spectral analyses.

EXAMPLE 1 Ethyl2-(4-(5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)propionate (1)

A mixture of 225.5 g of 4-chloro-3-nitrobenzotrifluoride and 109 g ofp-aminophenol in 500 ml of isopropyl alcohol was refluxed for 8 hours.Then 101 g of triethylamine was added, the mixture was refluxed for 2.5hours, then concentrated to dryness. The residue was treated with 1000ml of ether. The ethereal phase was separated, washed with water anddiluted with 600 ml of hexane. The resulting mixture was filteredthrough silica gel and the filtrate was concentrated to give4'-hydroxy-2-nitro-4-(trifluoromethyl)diphenylamine (1A), as a redsolid, m.p.: 130°-133° C.

A mixture of 29.8 g of 1A, 18.4 g of ethyl 2-bromopropionate, 14 g ofanhydrous potassium carbonate and 300 ml of 2-butanone was refluxed for6 hours, poured into water, and the resulting mixture was extracted withether. The extract was dried (MgSO₄), filtered and concentrated.Recrystallization of the residue from ether/hexane gave ethyl2-(4-(2-nitro-4-(trifluoromethyl)phenylamino)phenoxy)propionate (1B), asa crystalline solid, m.p.: 61°-63° C.

1B, in tetrahydrofuran, was treated with hydrogen (40 psi pressure in aParr-shaker, 10% palladium-on-carbon catalyst), to give ethyl2-(4-(2-amino-4-(trifluoromethyl)phenylamino)phenoxy)propionate (1C), asa solid, m.p.: 78° C.

5.3 g of 1C was dissolved in 50 ml of triethyl orthoformate, thesolution was refluxed for 1 hour, then concentrated under reducedpressure. The residue, an oil, was chromatographed over silica gel,using as eluent a 2:15:33 v/v/v mixture of tetrahydrofuran, ethylacetate and hexane (hereinafter, Solvent A), to give 1, as a viscousliquid.

1B also was prepared by an alternate method, as follows:

A mixture of 28 g of 4-nitrophenol, 36 g of ethyl 2-bromopropionate,27.6 g of potassium carbonate and 500 ml of butanone was stirred andrefluxed for 17 hours. The resulting mixture was diluted with 500 ml ofwater and extracted with ether. The extract was concentrated in a rotaryevaporator and the residue was recrystallized from ether-hexane to giveethyl 2-(4-nitrophenoxy)ropionate (1D), as a yellow solid, m.p.: 55°-56°C.

Hydrogenation of 1D (as described in preparation of 1C) gave ethyl2-(4-aminophenoxy)propionte (1E), as a viscous oil.

A solution of 209 g of 1E, 111 g of triethylamine and 225.5 g of4-chloro-3-nitrobenzotrifluoride in 600 ml of 2-butanone was refluxedfor 24 hours, then concentrated in a rotary evaporator. The oily residuewas dissolved in 1200 ml of ether; the solution was washed with water,dried (MgSO₄) and concentrated. Purification by silica gelchromatography (eluent: Solvent A) gave 1B.

EXAMPLE 2 2-(4-(5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)propionicacid (2)

A mixture of 3.7 g of 1, 0.39 g of sodium hydroxide and 50 ml of ethanolwas refluxed for two hours, then it was cooled to room temperature,acidified with hydrochloric acid and extracted with ether. Concentrationof the ether extract gave 2, as a white solid, m.p.: 181°-182° C.

EXAMPLES 3 and 4 Ethyl2-(4-(2-methyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)propionate(3). Ethyl2-(4-(2-ethyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)propionate(4)

3 was prepared, as an oil, from 1C and triethyl orthoacetate, and 4 wasprepared, as a solid, m.p.: 66°-68° C., from 1C and triethylorthopropionate by the procedures described in Example 1.

EXAMPLE 52-(4-(2-methyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)propionicacid (5)

5 was prepared, as a solid, m.p.: 107° C., from 3 by the procedure shownin the last step of the procedure described in Example 1.

EXAMPLE 6 Ethyl2-(4-(2-methyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)butyrate (6)

A mixture of 14.9 g of 1A, 14.8 g of ethyl 2-bromobutyrate, 18.8 g ofpotassium carbonate and 150 ml of butanone was stirred and refluxed for8 hours. The mixture then was diluted with water, acidified withhydrochloric acid and extracted with ether. The ether extract was dried(MgSO₄), filtered and concentrated in a rotary evaporator to give ethyl2-(4-(2-nitro-4-(trifluoromethyl)phenylamino)phenoxy)butyrate (6A), as aviscous oil.

Hydrogenation of 6A as described in Example 1 gave ethyl2-(4-(2-amino-4-(trifluoromethyl)phenylamino)phenoxy)-butyrate (6B), asa viscous oil.

A solution of 7 g of 6B in 50 ml of triethyl orthoacetate was heated at140° C. for 2 hours. The resulting mixture was cooled to roomtemperature, absorbed on silica gel and chromatographed, using theeluent described in Example 1, to give 6, as a viscous oil.

EXAMPLE 7 Ethyl2-(4-(5-trifluoromethyl)benzimidazol-1-yl)phenoxy)butyrate (7)

7 was prepared, as an oil, from 6B and triethyl orthoformate, by theprocedure described for the preparation of 6 from 6B.

EXAMPLE 82-(4-(2-methyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)butyric acid(8)

A mixture of 4.0 g of 6 and 0.4 g of sodium hydroxide in 50 ml of 50%ethanol was refluxed for 45 minutes, then concentrated to dryness. Theresidue was mixed with water, the mixture was acidified withhydrochloric acid and extracted with ether. The ether was evaporatedfrom the extract and the residue was recrystallized from ether-hexane togive 8, as a white solid, m.p.: 98° C.

EXAMPLE 9 2-(4-(5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)butyricacid (9)

9 was prepared, as a solid, m.p.: 214°-215° C., from 7, by the proceduredescribed in Example 8.

EXAMPLE 10 Methyl2-(4-(2-methyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)-3-methoxypropionate(10)

480 g of mercuric acetate was added to a solution of 139 g of methylacrylate in 170 ml of methanol. The resulting mixture was stirred for 3days at room temperature. To the mixture, cooled by an ice bath, asolution of 100 g of potassium bromide in 600 ml of water was added. Aheavy oil formed, was separated from the mixture and was extracted withchloroform. The extract was washed with water, dried (MgSO₄) andfiltered. The filtrate was heated to 60° C. and 36.9 g of bromine wasadded, drop-by-drop over a 2-hour period. The resulting mixture wascooled to 5° C. and concentrated in a rotary evaporator. The liquidresidue was distilled to give methyl 2-bromo-3-methoxypropionate (10A),b.p.: 69°-72° C. (3-5 Torr.).

A mixture of 69 g of 10A, and 104 g of 1A, 45 g of potassium carbonateand 1000 ml of 2-butanone was stirred and refluxed for 3 days. Theproduct, methyl2-(4-(2-nitro-4-(trifluoromethyl)phenylamino)phenoxy)-3-methoxypropionate(10B), was obtained as a solid, m.p.: 57° C., by procedures describedfor the isolation of 1B.

A solution of 17 g of 10B in 100 ml of tetrahydrofuran was treated withhydrogen (40 psi hydrogen pressure, Parr-shaker, 10%palladium-on-charcoal catalyst) to give methyl2-(4-(2-amino-4-(trifluoromethyl)phenylamino)phenoxy)-3-methoxypropionate(10C), as an oil.

A solution of 7 g of 10C in 25 ml of triethyl orthoacetate was refluxedfor 4 hours. The resulting mixture was concentrated in a rotaryevaporator and chromatographed over silica gel to give 10, as a viscousoil.

EXAMPLE 112-(4-(2-methyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)-3-methoxypropionicacid (11)

A solution of 4.5 g of 10 and 0.5 g of sodium hydroxide in 50 ml ofaqueous methanol was refluxed for 2 hours. The resulting mixture wasconcentrated to dryness, the residue was acidified with dilutehydrochloric acid and extracted with ether. The extract was dried andconcentrated. The residue was crystallized from ether-hexane to give 11,as a light tan crystalline solid, m.p.: 111°-112° C.

EXAMPLE 12 Ethyl4-(4-(2-methyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)pentanoate(12)

A mixture of 56.2 g of trans-2-pentenoic acid and 100 g ofN-bromosuccinimide in 1000 ml of carbon tetrachloride was stirred andrefluxed for 24 hours. The resulting mixture was cooled to roomtemperature and filtered. The filtrate was concentrated to a volume ofabout 300 ml, cooled to room temperature and filtered to givetrans-4-bromo-2-pentenoic acid, as a white crystalline solid (12A),m.p.: 78°-80° C.

25 g of hydrogen chloride was introduced into a solution of 139.2 g of12A in 1000 ml of ethanol. The resulting mixture was refluxed for 36hours, concentrated in a rotary evaporator, mixed with ice water andextracted with ether. The extract was washed to neutrality with aqueoussodium bicarbonate, dried (MgSO₄) and concentrated. The liquid residuewas fractionally distilled to give ethyl 4-bromo-2-pentenoate (12B), asa colorless liquid, b.p.: 82° C. (1.8 Torr.).

A mixture of 71.5 g of 1A, 45.0 g of 12B, 33 g of potassium carbonateand 800 ml of 2-butanone was stirred and refluxed for 24 hours. Theresulting mixture was divided in half. One half was concentrated todryness, the residue was diluted with ether and shaken with 2.5% sodiumhydroxide solution. The ether phase was separated, the ether wasevaporated, and the residue was chromatographed over silica gel to giveethyl 4-(4-(2-nitro-4-(trifluoromethyl)phenylamino)phenoxy)-2-pentenoate(12C), as a viscous oil.

23 g of 12B and 16.8 g of potassium carbonate were added to the secondhalf of the above mixture, and the resulting mixture was refluxed for 8hours. The mixture was concentrated to dryness, the residue was mixedwith ether and water, warmed, then cooled to room temperature andacidified with hydrochloric acid. The ether phase was separated,concentrated and chromatographed over silica gel to give4-(4-(2-nitro-4-(trifluoromethyl)phenylamino)phenoxy)-2-pentenoic acid(12D), as a viscous oil.

12D, in solution in tetrahydrofuran, was placed on a Parr shaker andtreated with hydrogen (40 psi hydrogen pressure, Parr shaker, 10%palladium-on-charcoal catalyst) to give4-(4-(2-amino-4-(trifluoromethyl)phenylamino)phenoxy)pentanoic acid(12E), as an oil.

A solution of 3.1 g of 12E in 50 ml of triethyl orthoacetate wasrefluxed for 2 hours. The resulting mixture was concentrated in a rotaryevaporator and the residue was chromatographed over silica gel to give12, as a viscous oil.

EXAMPLE 134-(4-(2-methyl-5-(trifluoromethyl)benzimidazol-1-yl)phenoxy)pentanoicacid (13)

A solution of 2.4 g of 12 and 0.25 g of sodium hydroxide in 50 ml ofaqueous ethanol was refluxed for one hour, and extracted with ether. Theextract was dried and concentrated. The residue was crystallized fromether-hexane to give 13, as a white solid, m.p.: 67°-68° C.

Compounds of Formula I have been found to affect the growth of plantsadversely, and therefore to be useful for controlling the growth ofunwanted plants. Individually, the compounds differ one from another intheir spectrum and level of phytotoxicity--some being more toxic tobroadleaved plants than to grasses, others vice versa; some beingnonactive when applied to the soil prior to emergence of the sproutingplants than when applied to the foliage of the growing plant, some viceversa.

Accordingly, the invention includes a method of controlling the growthof unwanted plants which comprises applying to the locus an effectiveamount of a compund of Formula I. Likewise, the invention includes plantgrowth control compositions comprising an inert carrier or asurface-active agent, or both a carrier and a surface-active agent, and,as active ingredient at least one compound of Formula I.

The term "carrier" as used herein means an inert solid or fluidmaterial, which may be inorganic or organic and of synthetic or naturalorigin, with which the active compound is mixed or formulated tofacilitate its application to the plant, seed, soil or other object tobe treated, or its storage transport or handling.

Suitable solid carriers are natural and synthetic clays and silicates,for example, natural silicas such as diatomaceous earth; magnesiumsilicates, for example, talcs, magnesium aluminum silicates, forexample, attapulgites and vermiculites; alumium silicates, for example,kaolinites, montmorillonites and micas; calcium carbonates; calciumsulfate; synthetic hydrated silicon oxides and synthetic calcium oraluminum silicates; elements such as, for example, carbon and sulfur;natural and synthetic resins such as, for example coumarone resins,polyvinyl chloride and styrene polymers and copolymers; bitumen, waxessuch as, for example, beeswax, paraffin wax, and chlorinated mineralswaxes; and solid fertilizers, for example, superphosphates.

Examples of suitable fluid carriers are water, dimethyl sulfoxide,alcohols, such as, for example, methanol, isopropyl alcohol, glycols;ketones such as for example, acetone, methyl ethyl ketone, methylisobutyl ketone, isophorone and cyclohexanone; ethers such as, forexample, cellosolves; aromatic hydrocarbons such as, for example,benzene, toluene and xylene; petroleum fractions such as, for example,herosene, light mineral oils; chlorinated hydrocarbons, such as, forexample, carbon tetrachloride, perchloroethylene, trichloroethane,including liquefied normall vaporous gaseous compounds. Mixtures ofdifferent liquids are often suitable. The surface-active agent may be anemulsifying agent or a dispersing agent or a wetting agent; it may benonionic or ionic any of the surface-active agents usually applied informulating herbicides or insecticides may be used. Examples of suitablesurface-active agents are sodium or calcium salts of polyacrylic acidsand lignin sulfonic acids; the condensation products of fatty acids oraliphatic amines or amides containing at least 12 carbon atoms in themolecule with ethylene oxide and/or propylene oxide; fatty acid estersof glycerol, sorbitan, sucrose or pentaerythritol; condensates of thesewith ethylene oxide and/or propylene oxide; sulfates or sulfonates ofthese condensation products, alkali or alkaline earth metal salts,preferably sodium salts, or sulfuric or sulfonic acid esters containingat least 10 carbon atoms in the molecule, for example, sodium laurylsulfate, sodium secondary alkyl sulfates, sodium salts of sulfonatedcastor oil and sodium alkyl-aryl sulfonates such as sodiumdodecylbenzene sulfonate; and polymers of ethylene oxide and copolymersof ethylene oxide and propylene oxides.

The compositions of the invention may be formulated as wettable powders,dusts, granules, solutions, emulsifiable concentrates, emulsions,suspension concentrates and aerosols. Wettable powders are usuallycompounded to contain 25, 50 or 75% by weight of toxicant and usuallycontain in addition to solid carrier, 3-10% by weight of a dispersingagent, 15% of a surface-active agent and where necessary, 0-10% byweight of stabilizer(s) and/or other additives such as penetrants orstickers. Dusts are usually formulated as a dust concentrate having asimilar composition to that of a wettable powder but without adispersant or surface-active agent, and are diluted in the field withfurther solid carrier to give a composition usually containing 1/2-10%by weight of toxicant. Granules are usually prepared to have a sizebetween 10 and 100 BS mesh (1.676-0.152 mm), and may be manufactured byagglomeration or impregnation techniques. Generally, granules willcontain 1/2-25% by weight toxicant and 0-1% by weight of additives suchas stabilizers, slow release modifiers and binding agents. Emulsifiableconcentrates usually contain, in addition to the solvent and, whennecessary, cosolvent, 10-50% weight per volume toxicant, 2-20% weightper volume emulsifiers and 0-20% weight per volume of appropriateadditives such as stabilizers, penetrants and corrosion inhibitors.Suspension concentrates are compounded so as to obtain a stable,nonsedimenting flowable product and usually contain 10-75% weighttoxicant, 0.5-5% weight of dispersing agents, 1-5% of surface-activeagent, 0.1-10% weight of suspending agents, such as defoamers, corrosioninhibitors, stabilizers, penetrants and stickers, and as carrier, wateror an organic liquid in which the toxicant is substantially insoluble;certain organic solids or inorganic salts may be dissolved in thecarrier to assist in preventing sedimentation or as antifreeze agentsfor water.

Aqueous dispersions and emulsions, for example, compositions obtained bydiluting a wettable powder or a concentrate according to the inventionwith water, also like within the scope of the present invention. Thesaid emulsions may be of the water-in-oil or of the oil-in-water type,and may have a thick mayonnaise-like consistency.

The compositions of the invention may also contain other ingredients,for example, other compounds possessing pesticidal, especiallyinsecticidal, acaricidal, herbicidal or fungicidal properties.

Protection of a locus or area from unwanted plants is effected byapplying a compound of Formula I, ordinarily in a composition of one ofthe aforementioned types, to the soil in which seeds of the unwantedplants are present, or to the foliage of the plants. The activecompound, of course, is applied in an amount sufficient to exert thedesired action.

The amount of compound of the invention to be used in controllingundesired plants will naturally depend on the condition of the plants,the degree of activity desired, the formulation used, the mode ofapplication, the climate, the season of the year, and other variables.Recommendations as to precise amounts are, therefore, not possible. Ingeneral, howevr, application to the locus to be protected of from 0.1 to10.0 kilograms per hectare of the compound of Formula I will besatisfactory.

EXAMPLES OF HERBICIDAL ACTIVITY

In the following examples, the species of plants that were tested were:

Barnyardgrass (watergrass)--Echinochloa crus-galli

Large crabgrass--Digitaria sanguinalis

Downy brome--Bromus tectorum

Yellow foxtail--Setaria lutescens

Redroot pigweed--Amaranthus retroflexus

Sicklepod--Cassia obtusifolia

Velvetleaf--Abutilon theophrasti

Garden cress--Lepidium sativum

Johnsongrass--Sorghum halepense

Test Procedures

The preemergence (soil) herbicidal activity of compounds of theinvention was evaluated by planting seeds of barnyardgrass, gardencress, downy brome, velvetleaf, yellow foxtail, and sicklepod in testtubes, nominally measuring 25×200 millimeters, filled aboutthree-quarters full of untreated soil, in each case covered on top withabout 2.5 cubic centimeters of soil treated with a certain amount of thetest compound. The treated soil applied to the tubes containing thebarnyardgrass and cress seeds contained one milligram of the testcompound per tube, and contained 0.1 milligram of the test compound pereach tube containing the seeds of the other plants. The dosages wereapproximately 22 and 2.2 pounds of test compound per acre, respectively.The seeds were planted on top of the treated soil and covered with about1.5 cubic centimeters of untreated soil. The planted soil was held undercontrolled conditions and temperature, moisture, and light for 9 to 10days. The amounts of germination and growth in each tube were evaluatedon a 0 to 9 scale, the numeric ratings having the following meanings:

    ______________________________________                                        Rating Meaning                                                                ______________________________________                                        9      No living tissue                                                       8      Plant severely damaged and expected to die                             7      Plant badly damaged, but expected to live                              6      Moderate damage, but complete recovery expected                        5      Intermediate damage (probably unacceptable for crop                           plants)                                                                3-4    Observable damage                                                      1-2    Plant slightly affected, possibly by the chemical,                            possibly due to biological variability                                 0      No visible effect                                                      ______________________________________                                    

The postemergence (foliar) herbicidal activity of compounds of theinvention was evaluated by spraying 10-day-old large downy brome plantsin some cases, 6-day-old Johnsongrass plants in other cases, 9-day-oldvelvetleaf plants, 9-day-old yellow foxtail plants and 9-day-oldsicklepod plants to runoff with a liquid formulation of the testcompound. The crabgrass and pigweed plants were sprayed with 2.4milliliters of a 0.25% solution (about ten pounds of the test compoundper acre), and other plants were sprayed with 2.4 milliliters of a0.025% solution (about one pound of the test compound per acre). Thesprayed plants were held under controlled conditions of temperature,moisture and light for 7 to 8 days and the effect of the test compoundwas then evaluated visually, the results being rated on the 0 to 9 scaledescribed above.

Results of the preemergence and postemergence herbicidal activity testsconducted on the compounds of the invention are set forth in Table I.

                                      TABLE I                                     __________________________________________________________________________    HERBICIDAL ACTIVITY                                                           Preemergence                        Postemergence                                   Barnyard-                                                                           Garden                                                                             Downy                                                                              Velvet-                                                                            Yellow                                                                             Sickle-                                                                           Crab-                                                                              Pig-                                                                             Johnson-                                                                           Velvet-                                                                            Yellow                                                                             Sickle-            Compound                                                                            grass cress                                                                              brome                                                                              leaf foxtail                                                                            pod grass                                                                              weed                                                                             grass                                                                              leaf foxtail                                                                            pod                __________________________________________________________________________    1     6     6    0    0    0    0   9    8  7    2    4    5                  2     8     8    6    0    0    2   7    7  7    2    5    5                  3     7     4    0    2    0    0   9    9  9    2    8    2                  4     0     4    0    0    0    0   3    6  0    3    0    2                  5     9     6    5    3    5    2   8    7  8    2    6    1                  6     0     0    0    0    0    0   8    3  7    0    2    2                  7     0     5    0    0    0    0   7    6  3    2    2    2                  8     7     7    0    0    0    0   8    4  7    2    2    2                  9     7     8    0    0    0    0   1    2  1    0    0    2                  10    4     4    2    0    2    0   4    9  2    2    2    0                  11    0     2    --   0    0    0   3    5  0    3    0    0                  12    0     6    0    0    0    0   2    4  0    0    0    0                  13    0     0    0    0    0    0   5    9  4    0    0    0                  __________________________________________________________________________

I claim:
 1. A compound of the formula: ##STR10## wherein n is 1 and X istrifluoromethyl, R is hydrogen, methyl or ethyl, R¹ is methyl, ethyl ormethoxymethyl; m is 0, 1 or 2; and R² is hydrogen, alkyl of from one tofour carbon atoms, or when R² is hydrogen, an alkali metal, or ammonium(N(R³)₃), salt wherein each R³ is hydrogen or alkyl of from one to sixcarbon atoms.
 2. A compound according to claim 1 wherein n is one, Xrepresents the trifluoromethyl moiety, bonded to the ring at the5-position, R and R¹ each represents methyl, m is 0, and R² representshydrogen, methyl or ethyl.
 3. A composition adapted to control ofunwanted plants, comprising an effective amount of a compound of claim 1together with a carrier, a surface-active agent, or both.
 4. Acomposition according to claim 3 wherein the compound of claim 1 is onewherein the trifluoromethyl moiety is bonded to the ring at the5-position, R and R¹ each represents methyl, m is 0 and R² representhydrogen, methyl or ethyl.
 5. A method for controlling growth ofunwanted plants at a locus which comprises applying to that locus aneffective amount of a compound of claim
 1. 6. A method for controllinggrowth of unwanted plants at a locus which comprises applying to thatlocus an effective amount of a compound of claim 2.